1. Field of the Invention
The invention relates to document transport devices for use in document handling machines, and particularly to document transport devices utilizing a conveyor belt for transporting documents on-edge in a vertically-oriented, upright position.
2. Related Art
Document handling machines which convey mail on-edge, that is, where the plane of the mail item is vertical while it is conveyed by a horizontal belt, are well-known. A document handling machine of this type is taught in commonly-assigned U.S. Pat. No. 4,955,596, the entire disclosure of which is incorporated herein by reference. Generally, such machines convey a series of envelopes between stations which perform various operations, such as bar-code reading, bar-code printing, and sorting.
Because mail items are delivered to the machine in stacks, a feeder which singulates the stacks of mail into a series of end-to-end, vertically oriented, individual items is required. This conversion step often uses a ninety-degree change of direction in the envelope path, which is accomplished by a series of feed rollers oriented so as to feed in a direction perpendicular to the path of incoming stacks of documents. However, any deceleration of a document at the perpendicular feeding area, due, for example, to momentary sticking or jamming of one or more documents, is transferred to documents upstream of the perpendicular feeding area. The reason for this transfer is that the close proximity of documents causes back-pressures to travel in a direction reverse to the feeding direction of the incoming documents. At high machine throughput speeds, the extent of these back-pressures is great. As a result, inconsistency in the amount of pressure applied to the documents and in the spacing between documents causes jamming and other undesirable effects.